Electrical discharge device



May 9, 1933. Q SPAETH 1,908,648

ELECTRICAL DISCHARGE DEVICE Filed Oct. 25 1950 1 NVENTQR W By K? \AATTORNEY Patented May 9, 1933 UNITED STATES PATENT OFFICE CHARLESSIPAET'E, OF FLUSHING, NEW YORK, ASSIGNOR TO OF JERSEY CITY, NEW JERSEY,A CORPORATION or New YORK ELECTRICAL DISCHARGE DEVICE Application filedOctober 23, 1930. Serial No. 490,847.

This application is a continuation in part of my copending applicationSerial No. 343,- 873, filed March 2, 1929.

The invention relates to electrical discharge devices, particularly todevices used for purposes of illumination.

It is an object of the present invention to provide an electricaldischarge tube which is capable of producing a very eflicient white liht.

Another object is to provide an electrical discharge illuminating tubewherein the color characteristics of the emitted light may be readilymodified in a predetermined manner or be maintained constant at anydesired value.

A further object is the provision of an electrical discharge tubeoperating at high eificiency and adapted to produce a concentratedbrilliant light emission approximating sunlight.

In accordance with my invention a radiant energy emitting dischargedevice is constructed having a filling of gas at reduced pressure and aplurality of electrodes for conducting an electrical dischargetherethrough. For modifying the light emission from the device auxiliarymeans are arranged to add to the gas filling in the desired amounts anagent for modifying the radiation spectrum. This auxiliary device ispreferably in the form of a mercury reservoir provided with means forliberating vapor.

A preferred form of my invention for illuminating purposes comprises anenvelope containing an atmosphere of rare gas such as neon and having areservoir of mercury. An alkali metal electrode and a cooperatingelectrode of any desired kind. is provided for passing a dischargedirectly through the rare gas and another electrode is furnished forcausing a discharge to be passed to the mercury in order to vaporize it.In order to secure the desired characteristics of illumination from thedevice means, such as resistances, inductances or capacitances may beprovided for controlling the relative intensities of the discharges. Forliberating the mercury suitable heating means may be employed in placeof the auxiliary electrode.

This heating means may comprise an suitable source of external heat, butpre erably is in the form of a heating coil placed adjacent to themercury reservoir and adapted to be energized by the discharge current.

When it is desired to secure a white light approximating that ofsunlight, the filling of the envelope may be of neon gas used inconjunction with a reservoir or other means for supplying an exactlyproportioned amount of mercury vapor. It is advisable where the tube isto be operated over a relatively long period of time to maintain themercury va rizing means in operation at the correct 1ntensity during theentire operation of the device. It is, however, possible to start thedischarge through the rare gas column and then supply the necessaryquantity of mercury vapor for a short period of time, after which thedevice will continue to emit a white light for some time. As operationis continued the mercury is cleaned up, apparently either bycondensation, occlusion, absorption or some other phenomena and thelight emitted by the device gradually reverts to the characteristiccolor of the rare gas, which in the case of neon is substantially red.By operating the mercury vaporizing device at the correct intensitymercury vapor is supplied at the same rate at which it is used up andhence the color of the emitted light remains constant.

The alkali metal electrode is very important to the prolonged operationof the tube. This electrode appears to function as a clean-up agent forthe excess mercury within the main body of the tube. because when anelectrode of ordinary metal is used the tube turns entirely blue after arelatively short period of operation, and cannot be restored to itsoriginal mercury free color. During the operation of the dischargedevice a minute amount of mercury vapor is continuously generated by theauxiliary electrode and carried over into the main body of the tube,where it is excited by the main discharge current. When the excitingcurrent is cut olf this mercury vapor remains in the main tube andapparently forms an amalgam, or other association, with the alkali metalelectrode, of such character. that the mercury is not liberated from theelectrode NE-ABGA. CORPORATION. I

during future operation of the device. Without the alkali metal themercury vapor relatively quickly reaches such density in the main tubethatonly blue light is generated. The alkali also serves to reduce thecathode fall of potential. A single metal or alloy of alkali metal maybe used. I find it preferable to use an alloy of potassium and caesiumin the proportion of 90% to 10%. By using such a combination the cathodedrop may be made as low as volts. For commercial purposes potassium maybe used alone to save expense.

The operating area of the alkali metal cathode should be so proportionedwith respect to the discharge current that the current density will beof but moderate intensity, for example, 3 amperes per square inch orless so that large amounts of metallic vapor will not penetrate the maindischarge path and mask the spectrum thereof. The alkali metal should bemade the cathode during normal operation of the device for otherwise theexcess mercury vapor is not absorbed or prevented from acting, by themetal.

For producing other colors of light other monatomic gases, for example,helium, argon, zenon, crypton, may be used with mercury vapor, or one ofa mixture of thera-re gases of a given characteristic color emission maybe used in conjunction with the means for libcrating the vapor.

Other objects and advantages and the manner of obtaining them will bemade clear in the following specification and accompanying drawing.

The drawing shows a device constructed in accordance with my inventionwherein the modification of the emitted spectrum is obtained by heatinga quantity of spectrum modifying material.

Referring more particularly to the drawing, the figure illustrates anelectrical discharge tube comprising a light transmitting envelope 1filled with rare gas, such as neon, and having a pair of main dischargeelec trodes 2 and 3, the cathode 3 being of alkali metal and anode 2 ofany well-known type, having the usual lead-in wires. The pressure of thegaseous atmosphere may range anywhere from .1 to 50 millimeters. but Ifind it preferable to use a pressure in the neighborhood of 6millimeters. A reservoir for a quantity of mercury 4 is provided in theform of an appendix 5. For energizing the tube the main elctrodes 2 and3 are connected across a suitable source of direct current 13 by meansof conductors 6 and 7. Connected in series with the conductor 6 is anadjustable resistance 8. The mercury 4: is vaporized by means of aheating coil 11 included in series with the conductor 6 leading toelectrode 2, and the heating effect is controlled by means of a variableshunting resistance 12. By varying the amount of heat produced by thecoil 11, the efiect of the mercury vapor may be controlled.

In operation a current is caused to pass from the source 13 between thetwo electrodes 2 and 3, thereby energizing the filling of rare gas andcausing it to emit light having certain color characteristics. Forexample, where the rare gas is neon the light will be predominantly red.In order to modify these color characteristics the resistance 10 isadjusted so that a current passes through the heating coil 11 strongenough to vaporize a quantity of the mercury. The mercury vapordifl'uses through the gas in the envelope 1, emitting light rays of itscharacteristic blue color. By properly adjusting the resistance 12 it ispossible so to balance the blue rays emitted against the characteristiccolor of the rare gas as to produce a light emission of any desiredcolor. For example, where the rare gas is neon a proper adjustment ofthe resistances 12 may be made to cause the emission of white light, theblue rays of the mercury being complementary to the red rays of theneon. The resistances 8 and 12 serve also as ballast resistances forbalancing the negative resistance of the gaseous discharge path. Theseresistances should therefore never be cut entirely out of circuit as thedischarge current would increase to an excessive value. While themercury reservoir is illustrated as positioned near to one of the mainelectrodes it need not necessarily be so located. The device willlikewise be operative with the reservoir at other positions. By placingthe reservoir as shown the impedance of, its discharge path is maderelatively large.

It is well known that ordinary li ht tubes utilizing a filling of rareas are a apted to operate at only relatively low current densities andthat in order to secure life long enough for commercial purposes it hasbeen thought necessary to utilize electrodes operating at relatively lowcurrent densities. A device constructed in accordance with my inventionwill, on the contrary, operate at extremely high current densitieswithout excessive heating and without excessive deterioration.

Where neon gas and anauxiliary mercury electrode are used, as set forth,the color may be adjusted from the characteristic neon color, throughwhite, to the characteristic mercury color. The efliciency of tubesconstructed in accordance with my invention is extremely high. Forexample, when using neon gas with mercury vapor to produce a white lightthe amount of energy consumed is only about 0.20 watt per sphericalcandlepower. Because of this relatively hi h eificiency the amount ofheat generated %)y the device is correspondingly small.

Lamps of this type are substantially silent in'operation, especiallywhen direct current is used. They are therefore of great value where awhite, silent and relatively cool, high intensity illuminating source isdesired, as in the recording of synchronized sound pictures.

It will be obvious to those skilled in the art that the invention iscapable of a wide variet of modifications and adaptations and that t epresent disclosure is intended merely to illustrate its nature withoutlimiting its'soope which is set forth in the appended claim.

What I claim is:

A lamp comprising an envelope, a quantity of rare gas Within saidenvelope, an anode at one end of the envelope, a cathode at the otherend thereof, a mercury chamber having connection with said envelope, anelectric heater for said reservoir, said heater being coiled around saidreservoir, electric means connected with said heater for regulating theheat developed by said heater and thereby controlling the amount ofmercury vapor generated from said reservoir, an alkaline metal at thecathode end of said envelope, in spaced relation to said mercuryreservoir, whereby mercury vapor in regulated quantities is supplied tothe rare gas to modify the color thereof and mercury va or isremovednear the cathode end from t e sphere of the light column by thesaid alkaline metal.

In testimony whereof: I have signed my name to this specification this21st day of October, 1930. 7

CHARLES SPAETH.

